Mayor de Blasio’s headed back to DC for yet another bite at the national-progressive-leadership apple. But is he really a progressive at all?

Friday morning, the mayor will speak at an event on “Forging a New Alliance: the Progressive Movement and the Socially Conscious Business Community.”

Funny: De Blasio’s “alliance” with business back home seems to consist largely of taking donations for his pet nonprofit, the Campaign for One New York, from firms with business before the city. Where’s the “social conscience” in that?

Anyway, he’s lucky on one front: Threats of inclement weather postponed today’s planned “Rally for School Equality” to next week. That means the mayor won’t be flaunting his progressivism just days after 15,000 parents march to demand an end to the racial and economic injustice of de Blasio’s public-school system.

Still, the school-equality crusaders already flagged the issue with the “Tale of Two Boys” ad we mentioned Tuesday. The point is that the system overwhelmingly sends less-well-off children — mostly black and Hispanic — to failed primary schools, which puts the kids on track to attend failed schools all the way through 12th grade.

Schools in better-off ’hoods work because the parents insist on it, and they have the means to make their voices heard. So the system dumps the incompetent teachers, principals and staff on the neighborhoods where angry parents can safely be ignored.

No, de Blasio didn’t create that injustice: It’s been building for decades, as so many city schools became cogs in the United Federation of Teachers’ jobs-protection program, where every union-compliant institution is by definition a success.

But the mayor has embraced that obscene status quo. He’s rewarded the UFT with a fat contract that reduced classroom-instruction time. His hand-picked schools chancellor jumps when the UFT says “frog.” His recent promises of pie-in-the-sky improvement all have due-by dates years in the future.

And he’s done all he can to crush the charter schools that offer actual education to the city’s poor. Charters are largely non-union, you see — and their success is a great embarrassment to the UFT.

We’ve questioned the mayor’s progressivism on other fronts. But it’s his embrace of this ongoing fraud — a system that only pretends to try to educate the poor — that most clearly stands against progress, against the glaring needs of the less well-off and with the special interests that feed off the public fisc.